text: More generally, atoms or atom groups that can form three or more non-equivalent single bonds (such as the transition metals in coordination compounds) may give rise to multiple stereoisomers when different atoms or groups are attached at those positions. The same is true if a center with six or more equivalent bonds has two or more substituents.
  For instance, in the compound , the bonds from the phosphorus atom to the five halogens have approximately trigonal bipyramidal geometry. Thus two stereoisomers with that formula are possible, depending on whether the chlorine atom occupies one of the two "axial" positions, or one of the three "equatorial" positions.
  For the compound , three isomers are possible, with zero, one, or two chlorines in the axial positions.
  As another example, a complex with a formula like , where the central atom M forms six bonds with octahedral geometry, has at least two facial–meridional isomers, depending on whether the three  bonds (and thus also the three  bonds) are directed at the three corners of one face of the octahedron (fac isomer), or lie on the same equatorial or "meridian" plane of it (mer isomer).